The present invention relates generally to an apparatus for treating a traveling textile material, either filaments or other strand-like material in tows, warps, or single filaments, and, more particularly, to an apparatus for heating traveling textile material to a heat-set or draw point localization temperature in a pressurized saturated or superheated steam atmosphere, such as preliminary to a texturizing or crimping operation, or otherwise to help stabilize the draw point conditions in a synthetic fiber draw process.
In a typical conventional apparatus for drawing, annealing and texturizing textile material, a heating apparatus is provided through which the strand is directed to travel preliminarily to elevate the temperature of the strand to a predetermined draw point or heat-set temperature. Typically, such strands are stretched with a localized draw point for uniform stretching to increase the tenacity of the fabric. After stretching, the strands undergo annealing or heat setting to stabilize the fibers after the draw point to set the fibers and reduce shrinkage to improve fiber uniformity and reliability.
One of the more common heating apparatus utilized for this purpose is a contact heater wherein the strand travels over a heating plate or heated rolls whose temperature are controlled to approximate the desired heat-set temperature. The temperature to which the strand is heated is a function not only of the temperature of the heating plate or roll itself, but also the time spent by a strand portion within the heater, which is determined by the traveling speed of the strand and the length of the heating plate, or the contact length of the rolls.
In recent years, the textile industry has increasingly demanded draw-texturizing/crimping equipment capable of operating at ever higher strand traveling speeds, which objective has been addressed in basically two ways. First, draw-texturizing/crimping equipment has been offered with heating apparatus of increasing lengths so as to prolong fabric Contact with the heaters and, in turn, sufficient heating to a desired heat-set temperature at increased strand traveling speeds. Secondly, draw-texturizing/crimping equipment has become available utilizing heaters which generate a considerably higher strand-heating temperature than the desired heat-set temperature so as to accomplish sufficient strand heating within a shorter strand traveling distance while the strand travels at an increased rate of speed. In a typical conventional apparatus for drawing and heatsetting textile strands, the strands are heated by hot air, steam at atmospheric pressure, heated rolls or hot plates.
Disadvantages exist in all types of heating apparatus, particularly the hot plate and roll annealer because of their space requirements, high cost, difficulty of surface cleaning from oligomers and finish oils and melting at machine stops. Problems also exist with hot air ovens and atmospheric steam ducts due to their ineffective heat transfer capabilities which typically result in very large machines.
In texturizing equipment utilizing shorter length heaters operable at more elevated temperatures, often in the range of up to 600.degree. C., substantially greater energy must be generated to accomplish heating to such elevated temperatures, thereby correspondingly increasing the cost of equipment operation. Further, a greater risk exists in operating such equipment that the cross section of the textile material can be rendered non-uniform by crystallizing the outermost portions of the strand to a greater degree than the strand core. In addition, due to periodic stoppages of the equipment, further damage to the material may occur by melting caused by prolonged contact with the heater. Therefore, it is critical in such equipment that the temperature of the heater and the traveling speed of the strand be closely monitored and carefully controlled to minimize these risks.
Similar disadvantages exist in conventional commercial equipment for heat-setting carpet yarns, wherein the objective is to stabilize the yarn bulk, to return the yarn to a fully relaxed state by relieving inner molecular tension within the yarn structure, and to increase its crystalinity for better and more uniform die pickup. For this purpose, commercial yarn heat-setting equipment typically accomplish heat setting by directing the yarn to travel in a low tensioned state through a dry heat atmosphere or in a steam atmosphere at ambient pressure or a slightly elevated pressure. However, since the steam atmosphere generated in such equipment is typically at a temperature below a desired heat-setting temperature and since heat transfer from a dry heat atmosphere to a traveling strand is relatively inefficient, such conventional heat-setting equipment must be of a relatively significant length to achieve a sufficient dwell time of the traveling carpet yarn within the heater to obtain the desired heat-setting results.